This invention relates to reprographic systems and more particularly to an automatic document handler including a scanner with an imaging lens and a photodetector device, such as a CCD array. The invention is more particularly directed to such a system which is adapted to copy original documents of two different sizes, such as a nominal 81/2" in width and a nominal 11" width.
A document handler to which the present invention may be applied is described in the co-pending application of Davis et al, Ser. No. 355,826 filed Mar. 8, 1982, U.S. Pat. No. 4,429,333. The document handler of that application system is adopted to handle either individual sheets or bound documents, and generates corresponding scanning signals which are suitable for loading into a memory. Once loaded into memory, the scanned information may then be used for controlling the operation of a programmable printing device.
The document scanning system incorporates a platen for scanning bulky documents, such as books, and further incorporates two exposing stations or fixed platens for scanning the two sides of sheet-type documents. The platen for bulky documents and the two exposing stations are positioned in a common plane. When the apparatus is scanning a bulky document at the scanning platen, the scanning carriage is moved by a drive at a constant velocity along the length of the platen. However, when the scanning carriage is operating to scan individual sheet-type documents, the carriage is positioned at one or the other of the fixed scanning platens, and the automatic document handling apparatus moves the sheet document past the fixed stations at a constant velocity. Where simplex copying of an original sheet document is required, the carriage remains at one of the fixed platens which may be considered as a home position. When both sides of the sheet document are to be copied, the carriage first scans the document at one of the fixed platens and then moves to the other fixed platen, for duplex copying of the same document.
The scanning carriage itself is movable along guideways which are at least coextensive with and parallel to the three platens mentioned above. The carriage includes lamps for illuminating the documents, a folding mirror, and a lens assembly including a lens and a photoelectric pick-up array.
In such scanning apparatus, particularly automatic document handling machines, it is desirable to use a single lens and a single photoelectric pick-up, such as a CCD array, for scanning in both the narrow and wide fields of view. Since the fields of view are defined by a generally common margin along one edge, it is necessary to move the lens assembly on the carriage along the optical axis to either narrow or widen the field of view and, at the same time, to move the lens assembly in translation, that is, in a direction normal to the optical axis, so that the optical center of the lens is always at or near the center of the particular field of view which has been selected. It is also desirable that this change in lens fields be accomplished promptly and reliably on command.